1. Field of the Invention
The present invention relates to a conductive paste used for formation of external electrodes of multilayered ceramic capacitors, and a multilayered ceramic capacitor employing the same.
2. Description of the Prior Art
In general, external electrodes of multilayered ceramic capacitors are produced by applying a conductive paste on a multilayered capacitor chip, drying the conductive paste layers on the chip, firing them to form conductive underlayers of the electrodes as well as to remove organic components contained in the paste, and then plating the conductive layers with nickel, and tin or solder.
The conductive paste used for such a purpose is usually prepared by dispersing conductive powder (e.g., Ag) and glass frit such as lead glass, zinc glass, or borosilicate glass in an organic vehicle dissolved in an organic solvent.
However, the external electrodes of the prior art frequently involve some problems which are caused by the plating solution seeping into the ceramic layers during plating. For example, the plating procedure causes a decrease in adhesion of the external electrodes of the multilayered ceramic capacitor and in resistance to flexure of the substrate on which the ceramic chip capacitor is mounted, and cracks of the ceramic layers due to heat shock.
To solve such problems, it has been proposed to increase the content of glass frit in the conductive paste or to use a chemically stable glass frit with a high-melting point for the purpose of protecting the ceramic layers from seepage of the plating solution during plating. However, a large amount of glass frit or use of high-melting point glass frit causes cracks in the ceramic layers of the capacitor chip during baking step and a decrease in the plating properties. In particular, if the dielectric ceramic layers are of a lead oxide-containing ceramic composition, they lose in their characteristics as they react with glass frit in the conductive paste layers when the external electrodes are baked at high temperatures, resulting in decrease of the capacitor characteristics.